Over the past several years remarkable progress has been made in assessing the development of infant memory by means of behavioral techniques. Thus, not only is there evidence of habituation to and discrimination of countour at birth, but also of simple forms by one or two months of age, and short-and long-term memory for complex patterns and categories by five or six months. Unfortunately, the development study of the electrophysiological correlates of infant memory has not kept pace with the behavioral data, although late components in the event-related potential (ERP) are a response to infrequent or novel stimuli, and thus an index of discrimination and memory. Only three studies have examined late potentials in the ERP to infrequently-occurring stimuli: Courchesne et al. found only a late negative frontal component, Nc, approximately 700 msec after stimulus onset, that correlated with infrequency. On the other hand, Hofmann and Salapatek, and Hofmann, Salapatek and Kuskowski observed only a positive occipital component, LPC, beginning at approximately 300 msec after stimulus onset, that also correlated with infrequency. In the first study of the current proposal, an experiment is proposed to reconcile these findings by recording from multiple scalp leads and extending the ERP sampling epoch to encompass the Courchesne and Hofmann et al. studies. A second set of experiments will examine whether late potentials are modality specific with respect to scalp location by presenting infrequent auditory vs. infrequent visual events. A third set of studies will examine infant categorization by looking for late potentials associated with an infrequent category identical stimulus will also be analyzed in a fourth study to see if a characteristic late potential occurs, indicating expectancy, and whether this late potential differs from that to a novel stimulus. It is our intention through the proposed studies to elucidate the development of infant memory and perception, and to refine electrophysiological measures of studying such abilities.